Pyrolysis Process as a Sustainable Management Option of Poultry Manure: Characterization of the Derived Biochars and Assessment of their Nutrient Release Capacities

Abstract

Raw poultry manure (RPM) and its derived biochars at temperatures of 400 (B400) and 600 ◦C (B600) were physico-chemically characterized, and their ability to release nutrients was assessed under static conditions. The experimental results showed that RPM pyrolysis operation significantlyaffectsitsmorphology,surfacecharges,andarea,aswellasitsfunctionalgroupscontents, which in turn influences its nutrient release ability. The batch experiments indicated that nutrient release from the RPM as well as biochars attains a pseudo-equilibrium state after a contact time of about 48 h. RPM pyrolysis increased phosphorus stability in residual biochars and, in contrast, transformed potassium to a more leachable form. For instance, at this contact time, P- and K-released amounts passed from 5.1 and 25.6 mg g−1 for RPM to only 3.8 and more than 43.3 mg g−1 for B400, respectively. On the other hand, six successive leaching batch experiments with a duration of 48 h eachshowedthatPandKreleasefromtheproducedbiocharswasaveryslowprocesssincenegligible amounts continued to be released even after a total duration of 12 days. All these results suggest that RPM-derived biochars have specific physico-chemical characteristics allowing them to be used in agriculture as low-cost and slow-release fertilizers.